A study was conducted to evaluate the effects of continuous pitch and speech tempo modifications on perceptual speaker verification performance by familiar and unfamiliar naive listeners. Speech recordings made by twelve male, native-French speakers were organised into three groups of four (two in-set, one out-of-set). Two groups of listeners participated, where one group was familiar with one in-set speaker group, while both groups were unfamiliar with the remaining in- and out-of-set speaker groups. Pitch and speech tempo were continuously modified, such that the first 75% of words spoken were modified with percentages of modification beginning at 100% and decaying linearly to 0%. Pitch modifications began at ± 600 cents, while speech tempo modifications started with word durations scaled 1:2 or 3:2. Participants evaluated a series of “go/no-go” task trials, where they were presented a modified speech recording with a face and tasked to respond as quickly as possible if they judged the stimuli to be continuous. The major findings revealed listeners overcame higher percentages of modification when presented familiar speaker stimuli. Familiar listeners outperformed unfamiliar listeners when evaluating continuously modified speech tempo stimuli, however, this effect was speaker-specific for pitch modified stimuli. Contrasting effects of modification direction were also observed. The findings suggest pitch is more useful to listeners when verifying familiar and unfamiliar voices.